Rapid and Environmentally Benign Synthesis of Polyhydroquinolines Using DBUST-Cl as a New Solid-Phase Catalyst

A novel solid-state ionic liquid catalyst, 4-sulfo-2,3,4,5,6,7,8,9-octahydroimidazo1,2-aazepin-4-ium chloride (DBUST-Cl), was synthesized from readily available reagents under mild conditions. A green, one-pot, multicomponent procedure for the preparation of polyhydroquinoline derivatives was developed using DBUST-Cl. The condensation of aromatic aldehydes, ethyl acetoacetate, 5,5-dimethylcyclohexane-1,3-dione, and ammonium acetate in ethanol at ambient temperature (25–35°C) proceeded to completion within 2 h, affording the products in 72–97% yield. The structures of DBUST-Cl and the synthesized polyhydroquinolines were confirmed by FTIR, 1H and 13C NMR, and ESI-MS spectroscopic analyses.